Durable 3d geometry conformal anti-reflection coating

ABSTRACT

Methods and systems for depositing a thin film are disclosed. The methods and systems can be used to deposit a film having a uniform thickness on a substrate surface that has a non-planar three-dimensional geometry, such as a curved surface. The methods involve the use of a deposition source that has a shape in accordance with the non-planar three-dimensional geometry of the substrate surface. In some embodiments, multiple layers of films are deposited onto each other forming multi-layered coatings. In some embodiments, the multi-layered coatings are antireflective (AR) coatings for windows or lenses.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of International Application No. PCT/US14/57424,with an international filing date of Sep. 25, 2014, entitled “Durable 3DGeometry Conformal Anti-Reflection Coating”, which is incorporatedherein by reference in its entirety.

FIELD

This disclosure relates generally to anti-reflective (AR) coatings andmethods for forming the same. In particular embodiments, systems andmethods for forming AR coatings on surfaces having three-dimensionalgeometries, such as curved surfaces, are described.

BACKGROUND

Anti-reflective (AR) coatings are generally applied to surfaces oflenses or windows to reduce the reflection of light incident on thesurfaces that can cause glare. Typically, the AR coatings are thin filmsstructures that are applied to surfaces using deposition techniques suchas sputter deposition, chemical vapor deposition (CVD) and plasmaenhanced chemical vapor deposition (PECVD) processes. In some cases, theAR coatings include multiple alternating layers of thin films, whichprovide materials of different refractive indexes and that improve theanti-reflective qualities of the AR coatings.

In some applications, the surface of a lens or a window has athree-dimensional geometry that makes applying a uniformly thick ARcoating difficult. In some applications, CVD processes can offer theability to conformally coat three-dimensional geometry parts. This isbecause CVD deposition of thin films occurs due to a chemical reactionat the surface of a part, while some other deposition technologiesinvolve physical or chemical reaction in the gas phase and transport ofchemical species to the substrate. However, many films formed usingtraditional CVD techniques are not adequately dense or durable forcertain applications, such as AR coatings for exterior surfaces ofconsumer products.

SUMMARY

This paper describes various embodiments that relate to anti-reflective(AR) coatings and methods for forming the same. The systems and methodsdescribed are used to form AR coatings on curved surfaces or surfacesotherwise having three-dimensional geometries.

According to one embodiment, a method of depositing a film on a curvedsurface of a substrate is described. The method includes positioning thecurved surface with respect to a source of a deposition system. Thesource includes an effective surface having a curved shape in accordancewith the curved surface of the substrate. The method also includescausing the source to emit particles such that the particles becomedeposited on the curved surface as the film. The curved shape of theeffective surface is associated with a thickness uniformity of the film.

According to another embodiment, a deposition system for depositing afilm on a surface of a substrate is described. The surface ischaracterized as having a non-planar shape. The deposition systemincludes a source that has an effective surface configured to emitparticles. The effective surface has a non-planar shape in accordancewith the non-planar shape of the surface of the substrate. Thedeposition system also includes a support configured to position thesubstrate with respect to the source such that the particles emittedfrom the source deposit as the film on the surface of the substrate. Thenon-planar shape of the effective surface is associated with a thicknessuniformity of the film.

According to a further embodiment, a plasma enhanced chemical vapordeposition (PECVD) apparatus for depositing a film on a curved surfaceof a substrate is described. The PECVD apparatus includes a hollowcathode source that has an effective surface configured to emit ions.The effective surface has a curved shape in accordance with a curvedshape of the curved surface of the substrate. The PECVD apparatus alsoincludes a support configured to position the substrate with respect tothe hollow cathode source such that the ions emitted from the sourcedeposit as the film on the curved surface of the substrate. The curvedshape of the effective surface is associated with a thickness uniformityof the film.

These and other embodiments will be described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be readily understood by the following detaileddescription in conjunction with the accompanying drawings, wherein likereference numerals designate like structural elements, and in which:

FIG. 1A shows a schematic view of a conventional deposition system usedto deposit a film on a planar surface.

FIG. 1B shows the conventional deposition system of FIG. 1A used todeposit a film on a non-planar surface.

FIG. 2A shows a schematic view of a deposition system used to deposit afilm on a non-planar surface in accordance with described embodiments.

FIG. 2B shows the deposition system of FIG. 2A used to deposit a secondfilm in accordance with described embodiments.

FIG. 2C shows a substrate that has multiple layers of film deposited ona non-planar surface in accordance with described embodiments.

FIG. 3 shows a schematic view of an alternate deposition system used todeposit a film on a non-planar surface in accordance with describedembodiments.

FIG. 4 shows a perspective view of one embodiment of a hollow cathodesource in accordance with described embodiments.

FIG. 5 shows a perspective view of one embodiment of a curved-shapedhollow cathode source in accordance with described embodiments.

FIGS. 6A and 6B show a schematic view of a hollow cathode systemarranged to uniformly deposit one or more films on substrates havingnon-planar surfaces in accordance with described embodiments.

FIG. 7 shows a schematic view of a hollow cathode system arranged inseries to uniformly deposit one or more films on substrates havingnon-planar surfaces in accordance with described embodiments.

FIG. 8 shows a schematic view of a hollow cathode system arranged inparallel to uniformly deposit one or more films on substrates havingnon-planar surfaces in accordance with described embodiments.

FIG. 9 shows a schematic view of a hollow cathode system having hollowcathode sources arranged in series and in parallel in accordance withdescribed embodiments.

FIG. 10 shows a flowchart that indicates a process for depositing a filmon a surface of a substrate in accordance with described embodiments.

DETAILED DESCRIPTION

Reference will now be made in detail to representative embodimentsillustrated in the accompanying drawings. It should be understood thatthe following descriptions are not intended to limit the embodiments toone preferred embodiment. To the contrary, they are intended to coveralternatives, modifications, and equivalents as can be included withinthe spirit and scope of the described embodiments as defined by theappended claims.

Described herein are methods and systems for depositing a thin film on asubstrate surface that has a three-dimensional geometry such that theresulting film is conformally deposited on the three-dimensionalgeometry and has a substantially uniform thickness. The methods involvedesigning a deposition source that mimics the three-dimensional surfacegeometry of the substrate. The deposition source can be positioned at asuitable distance to result in conformal coating on thethree-dimensional surface geometry of the substrate. In some cases,multiple layers of films are deposited onto each other formingmulti-layered coatings. In some embodiments, the multi-layered coatingsare antireflective (AR) coatings for windows or lenses.

According to some embodiments, a sputtering system is used and thedeposition source corresponds to a sputter target. According to otherembodiments, a plasma enhanced chemical vapor deposition (PECVD) systemis used and the deposition source corresponds to an ion source. In onespecific example, a hollow cathode source as part of a PECVD systemcapable of depositing Si₃N₄ and SiO₂ is used. Traditionally, this isdone with a planar-shaped source, resulting in a film having anon-uniform thickness. Embodiments herein describe a source with aneffective surface that has a curvature similar to the curvature ofsurface of substrate. In another specific example, a system of multiplesputtering sources angled appropriately to coat an entirethree-dimensional geometry of a substrate surface is described.Additionally, translation and/or rotation of the substrate duringcoating can be implemented to smooth out any non-uniformities.

Methods described herein are well suited for providing AR coatings onsurfaces of consumer products. For example, the methods described hereincan be used to form durable and effective AR coatings for portions ofcomputers, portable electronic devices and electronic deviceaccessories, such as those manufactured by Apple Inc., based inCupertino, Calif. In some embodiments, the methods described herein canbe used to form AR coatings on curved surfaces, such as curved windowsor lenses of consumer electronic devices.

These and other embodiments are discussed below with reference to FIGS.1-10. However, those skilled in the art will readily appreciate that thedetailed description given herein with respect to these Figures is forexplanatory purposes only and should not be construed as limiting.

As described above, conventional methods for forming AR coatings aredesigned for forming the AR coatings on flat or planar surfaces. FIG. 1Ashows a schematic view of system 100 used to deposit an AR coating on aplanar surface using a conventional thin film deposition technique.During a deposition process, substrate 102 is positioned withindeposition system 100. Deposition system 100 can correspond to, forexample, a sputter deposition system or a chemical vapor deposition(CVD) system, such as a plasma enhanced chemical vapor deposition(PECVD) system. Substrate 102 has surface 104 that is substantially flator planar in shape. Particles 106 from source 108 move toward anddeposit onto surface 104 of substrate 102 as film 112. Arrows 110indicate a general direction in which particles 106 move towardsubstrate 102 during a deposition process. As shown, particles 106 moveprimarily in a substantially perpendicular direction with respect tosurface 104.

In cases where system 100 is a sputter deposition system, source 108corresponds to a sputter target from which particles 106 are sputtered.In cases where system 100 is a CVD system, source 108 corresponds to asource of volatile material or precursor material that flows toward anddeposits onto surface 104. In a PECVD system, particles 106 correspondto ions and/or other reactive chemical species within a plasma. Usingsystem 100, film 112 can be deposited on surface 104 uniformly. That is,the thickness of film 112 can be about the same across surface 104.

FIG. 1B shows system 100 used to deposit a film on a non-planar surface.Substrate 114 includes surface 116 having a non-planar shape. Anon-planar surface is a surface having a three-dimensional geometry ortopography that is not substantially planar. Surface 116, in particular,has a curved shape. During a deposition process, particles 106 movetoward and deposit onto surface 116 as film 118. As shown, particles 106move substantially in the same direction with respect to each other, asindicated by arrows 110. Since surface 116 is curved, some particles 106do not deposit onto surface 116 at a perpendicular direction,particularly at edge portions 120. As a result, film 118 is depositedmore thinly at edge portions 120 compared to center portion 122. Thus,film 118 has a non-uniform thickness. If film 118 is a AR coating, thismeans that center portion 122 will function differently than edgeportions 120 with respect to anti-reflective effectiveness. For example,center portion 122 may work more effectively than edge portions 120 withrespect to anti-reflective effectiveness. If the deposition process istuned to deposit more material onto edge portions 120, center portion122 will be deposited on too thickly. This can result in edge portions120 of film 118 being more effective than center portion 122 withrespect to providing anti-reflective functionality. In addition toreduced anti-reflective functionality, portions of film 118 that are toothick or too thin can take on a color or hue rather than being fullytransparent, which can be undesirable in many applications. If multiplelayers of film (not shown) are deposited to form the final AR coating,this non-uniformity can be exacerbated resulting in even more disparitybetween thicknesses of edge portions 120 compared to center portion 122.

Methods and systems described herein can be used to form AR coatings onnon-planar surfaces in such a manner such that the resulting AR coatingshave substantially uniform thicknesses. FIG. 2A shows a schematic viewof system 200 used to form an AR coating on a non-planar surface using athin film deposition technique in accordance with described embodiments.Substrate 202 can be made of any suitable material. In some embodiments,substrate 202 is a window or lens that is made of glass or plastic, suchas for an electronic device or part of an electronic device. Substrate202 is placed in system 200 and positioned with respect to source 208such that particles 206 can be deposited onto surface 204 of substrate202. In some embodiments, substrate 202 is supported and positionedusing support 203. Surface 204 is non-planar in that surface 204 has athree-dimensional geometry or topography that is substantiallynon-planar. In some embodiments, surface 204 has a curvedthree-dimensional shape. That is, surface 204 can be curved in x, y andz directions. It should be noted that the methods described herein canbe used to form an AR coating having any suitable shape, includingsurfaces having multiple curved portions, planar portions and/or splineshaped portions.

Source 208 has effective surface 218 that corresponds to the surfacefrom which particles 206 are emitted. For example, in sputtering systemseffective surface 218 can correspond to a surface of a sputter target.In PECVD systems, effective surface 218 can correspond to a surface ofan ion source (e.g., hollow cathode source) that emits reactive chemicalspecies such as ions. According to described embodiments, effectivesurface 218 has a shape that substantially matches the shape of surface204 of substrate 202. For example, if surface 204 has a curved shape,effective surface 218 can have the same degree of curvature as surface204. In this way, effective surface 218 mimics the shape of surface 204of substrate 202. This configuration allows effective surface 218 to besubstantially equidistant to surface 204 at substantially all pointsalong surface 204. The size of effective surface 218 can vary dependingon the type of source (e.g., sputter target or ion source) and distanced between source 208 and surface 204 of substrate 202. In general,greater distance d will require effective surface 218 to be larger.

During a deposition process, particles 206 from source 208 move towardand deposit onto substrate 202 in a substantially perpendiculardirection with respect to surface 204, as indicated by arrows 210. Thatis, instead of particles 206 all moving in the same direction, asdescribed above with respect to FIGS. 1A and 1B, particles 206 convergetoward surface 204. This arrangement results in film 212 being depositedsubstantially uniformly and such that the final film 212 has asubstantially uniform thickness. That is, the thickness of film 212 isabout the same across surface 204, including at center portion 216 andedge portions 214. In some embodiments, substrate and/or source 208 isrotated or otherwise moved during a deposition process to smooth out anynon-uniformities. For example, a rotating mechanism (not shown) can becoupled to support 203 such that support 203 and substrate 202 arerotated along the y-axis during a deposition process.

System 200 can be any suitable deposition system. In some embodiments,system 200 is a sputter deposition system where source 208 correspondsto a sputter target from which particles 206 are sputtered. Thesputtering can be accomplished by introducing a sputter gas (not shown)such as argon gas, which impinges on sputter target source 208 creatingparticles 206. The material of a sputter target source 208 will dependupon a desired material of film 212. In some embodiments, the sputtertarget source 208 includes silicon such that film 212 containingsilicon, such as Si₃N₄ (silicon nitride) and/or SiO₂ (silicon dioxide).

In some embodiments, system 200 is a CVD system, such as a PECVD system.In embodiments where system 200 is a PECVD system, source 208 cancorrespond to an ion source that forms ions and/or other reactivespecies within a plasma. The type of reactive species can be controlledby choosing the appropriate reaction gas(es) supplied to source 208.Source 208 breaks up the reactive gas and discharges particles 206 inthe form of ions and/or other reactive species. The ions and/or otherreactive species can react with other species within the plasma beforedeposition. For example, silane (SiH_(x)) can be supplied into source208, where it is broken up into silicon species (Si_(x)H_(y)). Thesesilicon species can react with a nitrogen-containing gas (e.g., N₂,NH_(x)) to form a silicon nitride film. Alternatively, the siliconspecies can react with an oxygen-containing gas (e.g., NO_(x)) to form asilicon dioxide film. In particular embodiments, source 208 correspondsto a hollow cathode source of a PECVD system. Embodiments including ahollow cathode source will be described in detail below with respect toFIGS. 4 and 5.

Film 212 can be made of any suitable material. In some embodiments, film212 is made of a material suitable for an AR coating. For example, film212 can be substantially transparent or translucent such that substrate202 is visible therethrough. In some applications where the AR coatingis applied to a consumer product, the AR coating should be dense anddurable enough to substantially avoid damage and delamination duringnormal use of the consumer product. In particular embodiments, film 212includes Si₃N₄ (silicon nitride), SiO₂ (silicon dioxide), NB₂O₅, TiO₂(titanium oxide), TaO₂ (tantalum oxide) and/or other suitable AR filmmaterials. In some embodiments, one or more subsequently deposited filmsare deposited on film 212 using one or more subsequent depositionprocesses, which will be described below with respect to FIGS. 2B and2C.

Distance d between source 208 and surface 204 of substrate 202 can varydepending on a number of factors including the type of system 200. Ingeneral, the larger the distance d, the larger effective surface 218should be in order to achieve full coverage of surface 204. Inembodiments where system 200 is a sputter deposition system and source208 corresponds to a sputter target, distance d should be large enoughto allow room for a sputter gas to sputter off particles 206 from source(sputter target) 208, yet small enough for sufficient sputtering ontosurface 204. In embodiments where system 200 is a PECVD system andsource 208 corresponds to an ion source (e.g., hollow cathode source),distance d should be large enough to allow adequate formation anddischarge of ions and/or other reactive species. Generally, this meansdistance d for PECVD systems is generally smaller than for sputterdeposition systems. In some embodiments, distance d is very small suchthat particles 206 can be very evenly distributed and deposited ontosurface 204. The angle and/or position of surface 204 of substrate 202should be aligned relative to effective surface 218 to assure thatparticles 206 arrive at surface 204 substantially uniformly. Generally,the larger distance d is, the more accurately the angle and/or positionof surface 204 should be aligned relative to effective surface 218 inorder to achieve a uniformly thick film 212.

In some applications, single film 212 is sufficient. In otherembodiments, one or more subsequent layers are deposited onto film 212.For example, some AR coatings include multiple layers of thin filmshaving different refractive indexes, such as alternating layers ofsilicon nitride and silicon dioxide films. As described above,depositing more than one layer on a non-planar surface usingconventional deposition techniques can exacerbate any non-uniformity ofthe final AR coating if the individual films are not depositeduniformly. The methods described herein can be used to deposit more thanone layer of film onto a non-planar substrate such that a finalmulti-layered film has a uniform thickness.

FIG. 2B shows a schematic view of system 200 used to form amulti-layered film coating in accordance with described embodiments. Inparticular, system 200 is used to deposit a second film 222 onto film212. Second film 222 can include the same or different material as film212. For example, film 212 can include silicon dioxide and second film222 can include silicon nitride. As described above with respect to film212, the composition of second film 222 can be controlled by choosingthe type of material at source 208 and/or gases within system 200. Inembodiments where system 200 is a sputter deposition system where source208 corresponds to a sputter target, process conditions can be changedsuch that second film 222 has a different chemical composition than film212. In embodiments where system 200 is a PECVD system with source 208corresponding to an ion source, the reaction gas that is supplied tosource 208 can be changed to correspond to a desired film type. In somecases where films 212 and 222 are made of different materials, source208 can be purged between deposition processes.

Because source 208 has effective surface 218 having a shape thatcorresponds to surface 204, particles 220 move toward substrate 202 in asubstantially perpendicular direction, as indicated by arrows 210. Inthis way, second film 222 is uniformly deposited onto film 212. That is,the thickness of second film 222 at edge portions 224 is substantiallythe same as the thickness of second film 222 at center portion 226.After second film 222 is deposited, any suitable number of films cansubsequently deposited onto substrate 202 until a desired number filmsare deposited.

FIG. 2C shows substrate 202 after multiple layers of film are depositedto form multi-layered coating 228. In particular, multi-layered coating228 includes film 212, second film 222, third film 230 and fourth film232. Note that the number of film layers indicated in FIG. 2C arerepresentative of only some embodiments and any suitable number oflayers can be formed. Film 212, second film 222, third film 230 andfourth film 232 can each be made of the same or different materials. Ina particular embodiment, multi-layered coating 228 is an AR coating thatincludes alternating layers of material having different refractiveindexes. This arrangement can allow for the optimal destructiveinterference of light incident exposed surface 234, thereby reducingglare. For example, film 212 and third film 230 can be composed ofsilicon dioxide while second film 222 and fourth film 232 are composedof silicon nitride. In some embodiments, silicon nitride/silicon dioxideAR coatings are preferred because silicon nitride is relatively dense,durable and has a relatively high stiffness compared to some other ARcoating material alternatives and silicon dioxide bonds well withsilicon nitride bond since they each include base silicon matrixes.Thus, the silicon dioxide and silicon nitride film layers will be lessprone to pealing from each other when exposed to abrasion forcescompared to films made of more dissimilar materials. For at least thesereasons, silicon dioxide and silicon nitride AR coatings can be wellsuited for application on exposed surfaces of consumer products thatexposed to a lot of wear and abrasion.

The timing between depositing each of films 212, 222, 230 and 232 canvary depending on the deposition technique use as well as otherprocessing parameters. For example, in sputtering systems, eachsuccessive film can generally be deposited very soon after each previousfilm is deposited. In PECVD systems where films 212, 222, 230 and 232include different materials, it may be beneficial to allow time for thesource to adequately pump down and purge of a first reaction gas beforeintroducing a second type of reaction gas.

FIG. 3 shows a schematic view of system 300 used to form an AR coatingon a non-planar surface using an alternative thin film depositiontechnique in accordance with described embodiments. System 300 isconfigured to deposit film 312 on surface 304 of substrate 302. System300 can be any suitable deposition system configured to deposit film312, such as a sputter deposition system or PECVD system. Surface 304 isnon-planar (e.g., curved) and therefore difficult to deposit onto in auniform fashion using conventional techniques described above. System300 includes a series of sources 308 having elements a-g that arearranged to have effective surface 318 with a shape that closelycorresponds to the shape of surface 304 of substrate 302. In someembodiments, each of elements a-g can have a substantially planarsurface but collectively form effective surface 318 that roughly mimicsthe curved surface 304 of substrate 302. This series of sources 308 maybe easier to implement when it is difficult to obtain a single sourcehaving a shape that corresponds to surface 304, such as source 208described above with reference to FIGS. 2A and 2B. In some embodiments,system 300 includes support 303, which supports and positions substrate302 with respect to series of sources 308.

Series of sources 308 can include any suitable number of elements a-gand are not limited to the number of elements a-g shown. In general,series of sources 308 should have a suitable number of elements a-g forproviding film 312 having a sufficiently uniform thickness. This canvary depending on the type of system 300 (e.g., sputter or PECVD),distance d between series of sources 308, the three-dimensional geometryof surface 304, and particular application film uniformity requirements.In embodiments where system 300 is a sputter deposition system, elementsa-g can each correspond to a sputter target. In embodiments where system300 is a PECVD system, elements a-g can each correspond to an ionsource. Film 312 can be made of any suitable material, including Si₃N₄(silicon nitride), SiO₂ (silicon dioxide), NB₂O₅, TiO₂ (titanium oxide),TaO₂ (tantalum oxide) and/or other suitable AR film materials. System300 can be used to form subsequent layers of film, similar to describedabove with reference to FIGS. 2B and 2C.

As described above, in some embodiments a PECVD system using a hollowcathode source is used to deposit an AR film. FIG. 4 shows a perspectiveview of one embodiment of a hollow cathode source 400, which has alinear shape. Hollow cathode source 400 has a tubular shape thatincludes cavity 402. A radio frequency (RF) and/or other currentdischarge can be applied to hollow cathode source 400 as a gas passesthrough cavity 402 forming a plasma. For example, a silicon-containinggas, such as a silane gas, can be passed through cavity 402 to form aplasma with silicon-containing ions and reactive species. The ions andreactive species flow toward and deposit conformally onto a substratesurface as a film.

Since hollow cathode source 400 has a substantially linear shape, it canbe used to form a film having a substantially uniform surface on alinear or planar surface of a substrate, such as shown in FIG. 1A.However, use of a single linearly shaped hollow cathode source 400 todeposit onto a curved surface can cause the resultant film to have anon-uniform thickness, such as shown in FIG. 1B. To accommodate anon-planar substrate surface, two or more hollow cathode sources 400 canbe used in conjunction with other, such as shown in FIG. 3. Inparticular, the two or more hollow cathode sources 400 can form aneffective surface that mimics the non-planar surface of a substrate.This way, the ions and reactive species within the plasma can flowtoward the non-planar surface of the substrate in a substantiallyperpendicular direction with respect to the surface of the substrate,thereby forming a film having a substantially uniform thickness.

In some embodiments, the shape of a hollow cathode source is customizedto form an effective surface that mimics a non-planar surface of asubstrate. FIG. 5 shows hollow cathode source 500 having a curved shapeeffective surface 504 in accordance with some embodiments. Hollowcathode source 500 includes cavity 502 where a radio frequency (RF)and/or other current discharge is applied to a gas forming a plasmahaving ions and/or other reactive chemical species. The curved shapeeffective surface 504 mimics a shape of curved surface of a substrate,such as shown in FIGS. 2A-2D. The ions and/or other reactive species canthen flow toward the curved substrate in a substantially perpendiculardirection with respect to the curved substrate surface, thereby forminga film having a substantially uniform thickness.

Note that effective surface 504 of hollow cathode source 500 can haveany suitable shape in accordance with a shape of a substrate surface andis not limited to the curved shape shown in FIG. 5. In some embodiments,effective surface 504 mimics a two-dimensional surface of a substrate.In other embodiments, effective surface 504 mimics a three-dimensionalsurface of a substrate. In some embodiments, two or more hollow cathodesources 500 can have the same or different shaped effective surfaces 504are combined to mimic the shape of a substrate surface. In someembodiments, one or more non-planar shaped hollow cathode sources 500are combined with one or more linear shaped hollow cathode sources 400to mimic a three-dimensional shape of a substrate surface. Somecombinations of hollow cathode sources are described below withreference to FIGS. 6-9.

In some applications, a substrate surface has a relatively largethree-dimensional surface that is not easily covered using a singlehollow cathode source. FIGS. 6A and 6B show hollow cathode systems thatcan be used as part of a PECVD apparatus in order to uniformly depositfilms on substrates having relatively large surfaces. FIG. 6A shows aschematic view of hollow cathode system 600, which includes hollowcathode source 602 for depositing film 603 onto substrate 604. Substrate604 has surface 606 with a non-planar shape. In some embodiments,substrate 604 is a window or lens for an electronic device. In someembodiments, system 600 includes support 601, which supports andpositions substrate 604 relative to hollow cathode source 602. Surface606 is relatively large in that surface 606 substantially spans in x, yand z directions.

Hollow cathode source 602 has effective surface 610 that has a shape inaccordance with a portion of surface 606 of substrate 602. In order tocover surface 606 in its three-dimensional entirety, substrate 604 istranslated relative to hollow cathode source 602 during a depositionprocess, as indicated by arrow 608 (z direction). This way, hollowcathode source 602 can provide a plasma having ions and/or otherreactive species sufficiently proximate different regions of surface 606to deposit film 603 thereon at different times during the depositionprocess. In some embodiments, support 601 includes a translationalmechanism, such as a conveyor belt system, that translates substrate 604while hollow cathode source 602 remains stationary. In otherembodiments, hollow cathode source 602 is translated while substrate 604remains stationary. In other embodiments, both hollow cathode source 602and substrate 604 are translated and neither remains stationary.

In some embodiments, the rate at which substrate 604 is translatedrelative to hollow cathode source 602 is controlled in order to controlthe rate of deposition onto surface 606. For example, the rate oftranslation can be tuned such that film 603 has a predeterminedthickness. In general, the faster the translation, the thinner film 603will be. In some embodiments, the rate of translation is consistentthroughout a deposition process. In other embodiments, the rate oftranslation is varied during a deposition process. That is, the rate oftranslation can be increased or decreased at different points of thedeposition process. This technique can be used, for example, tocompensate for different regions of surface 606 being differentdistances from effective surface 610. For example, surface 606 atregions 612 and 614 are farther from effective surface 610 of hollowcathode source 602 compared to region 616 (i.e., in the y and xdirections). This varied distance can lead to film 603 having a greaterthickness at region 616 compared to regions 612 and 614. To provide film603 having a uniform thickness at region 616 and regions 612 and 614,the rate of translation can slower when effective surface 610 of hollowcathode source 602 is positioned over regions 612 and 614 and fasterwhen positioned over region 616. This can allow more dwell time anddepositing of more material at regions 612 and 614 to compensate for thegreater distance from effective surface 610. Resultant film 603 oversurface 606 will have a uniform thickness.

According to some embodiments, a flow rate of reaction gas provided tohollow cathode source 602 is varied in order to control the rate ofdeposition onto surface 606. Different flow rates can be implementedinstead of or in addition to varying a translation rate of substrate 604relative to hollow cathode source 602. In general, higher gas flow rateswill result in higher rates of deposition and lower gas flow rates willresult in lower rates of deposition. For example, a higher gas flow ratecan be applied when effective surface 610 of hollow cathode source 602is positioned over regions 612 and 614 and lower flow rate whenpositioned over region 616. This can compensate for the greater distanceof regions 612 and 614 from effective surface 610.

As described above, in some applications multiple layers of film aredeposited to form an AR coating. After a first deposition process usedto deposit film 603 is sufficiently complete, substrate 604 can beeither moved to a second hollow cathode source (not shown) to deposit asecond film, or substrate 604 can be transferred through hollow cathodesource 602 a second time. FIG. 6B shows hollow cathode system 600 duringa second deposition process where substrate 604 is transferred throughhollow cathode source 602 a second time. The second deposition processdeposits second film 616 onto the already deposited film 603. In oneembodiment, the second deposition process involves transferringsubstrate 604 through hollow cathode source 602 in an opposite direction(as indicated by arrow 618) compared to the first deposition process fordepositing film 603. In some embodiments, support 601 includes atranslational mechanism, such as a conveyer belt system, that translatessubstrate 604 while hollow cathode source 602. In other embodiments,hollow cathode source 602 is translated while substrate 604 remainsstationary.

In some embodiments, second film 616 includes substantially the samematerial as film 603. In other embodiments, second film 616 includes adifferent material than film 603. In cases where second film 616includes a different material, hollow cathode source 602 is configuredto form a first type of ions and/or other reactive chemical species whendepositing film 603 and a second type of ions and/or other reactivechemical species when depositing second film 616. For example, hollowcathode source 602 can be supplied with a first reaction gas to formfilm 603 of a silicon dioxide material and a second reaction gas to formsecond film 616 of a silicon nitride material, or vice versa.

In some embodiments, a number of hollow cathode sources are used inorder to uniformly cover a three-dimensional surface of a substrate.FIG. 7 shows a schematic view of hollow cathode system 700, whichincludes hollow cathode sources 702 a, 702 b, 702 c and 702 d arrangedin series for depositing film 703 onto substrate 704. In someembodiments, system 700 includes support 701 that supports and positionssubstrate 704 relative to hollow cathode sources 702 a, 702 b, 702 c and702 d. Substrate 704 has three-dimensional surface 606, which includesregions 712, 714 and 716.

Hollow cathode sources 702 a, 702 b, 702 c and 702 d each have effectivesurfaces 710 a, 710 b, 710 c and 710 d, respectively, that compensatefor the three-dimensional shape of surface 606. In particular, hollowcathode source 702 a has an offset position in the x and y directionscompared to each of hollow cathode sources 702 b and 702 c in order tobring hollow cathode source 702 a close enough region 714 of surface 706to provide film 703 the same thickness over region 714 as over region716. Similarly, hollow cathode source 704 d has an offset position inthe x and y directions compared to each of hollow cathode sources 702 band 702 c in order to bring hollow cathode source 702 a close enough toregion 712 of surface 706 to provide film 703 the same thickness overregion 712 as over region 716. The result is film 703 having a uniformthickness over regions 712, 714 and 716 of surface 706. In someembodiments, effective surfaces 710 a, 710 b, 710 c and 710 d are eachpositioned at the same distance from surface 706. In some embodiments,the flow of gas provided to each of hollow cathode sources 702 a, 702 b,702 c and 702 d is varied in order to control the rate of depositiononto different regions 712, 714 and 716 of surface 706. Note that anysuitable number of hollow cathode sources can be used in order toprovide a film 703 having a sufficiently uniform thickness.

In some cases, the relative positions of substrate 704 and cathodesources 702 a, 702 b, 702 c and 702 d can be changed. For example,support 701 can include a translational mechanism, such as a conveyorbelt system, that translates substrate 704 that accurately positionssubstrate 704 under hollow cathode sources 702 a, 702 b, 702 c and 702 dfor a deposition process and removes substrate 704 after a depositionprocess. In one embodiment, substrate 704 is translated in directions708 and 718. For example, substrate 704 can be translated in direction708 before a deposition process and then translated in direction 718after the deposition process is complete. In other embodiments,substrate is translated in direction 708 before and after a depositionprocess. In some embodiments, system 700 is used to deposit a secondfilm (not shown) onto film 703.

According to some embodiments, multiple substrates are processedsimultaneously, which may be beneficial in some manufacturing situationswhere throughput is an important factor. FIG. 8 shows a schematic viewof hollow cathode system 800, which includes hollow cathode sources 802a, 802 b and 802 c arranged in parallel for depositing films 803 a, 803b and 803 c onto substrates 804 a, 804 b and 804 c, respectively. Insome embodiments, system 800 includes supports 801 a, 801 b and 801 c,which support and position substrates 804 a, 804 b and 804 c,respectively. Hollow cathode source 802 a has effective surface 810 athat is in accordance with curved surface 806 a of substrate 804 a.Hollow cathode source 802 b has effective surface 810 b that is inaccordance with curved surface 806 b of substrate 804 b. Hollow cathodesource 802 c has effective surface 810 c that is in accordance withcurved surface 806 c of substrate 804 c. In some embodiments, the shapesof surfaces 806 a, 806 b and 806 c substrates 804 a, 804 b and 804 c arethe same. In other embodiments, one or more of surfaces 806 a, 806 b and806 c have different shapes.

As shown, hollow cathode sources 802 a, 802 b and 802 c are positionedin parallel such that substrates 804 a, 804 b and 804 c can be depositedonto simultaneously. For example, a translation mechanism can be used totranslate either substrates 804 a, 804 b and 804 c or cathode sources802 a, 802 b and 802 c in direction 808. In some embodiments, hollowcathode sources 802 a, 802 b and 802 c are all part of a single hollowcathode source that has curved portions to accommodate each ofsubstrates 804 a, 804 b and 804 c. If hollow cathode sources 802 a, 802b and 802 c are all part of a single hollow cathode source, a single gassource can be used to supply gas to hollow cathode sources 802 a, 802 band 802 c. In other embodiments, hollow cathode sources 802 a, 802 b and802 c are each separate hollow cathode sources that are supplied gas bydifferent gas sources. In some embodiments, system 800 is used todeposit second films (not shown) onto films 803 a, 803 b and 803 c by,for example, translating either 804 a, 804 b and 804 c or hollow cathodesources 802 a, 802 b and 802 c in direction 818 and changing the sourcegases supplied to hollow cathode sources 802 a, 802 b and 802 c.

As described above with respect to FIGS. 6A and 6B, the rate of relativetranslation of substrates 804 a, 804 b and 804 c with respect to hollowcathode sources 802 a, 802 b and 802 c can be varied in order tocompensate for the three-dimensional variation of surfaces 806 a, 806 band 806 c and in order to provide films 803 a, 803 b and 803 c havinguniform thicknesses. For example, the rate of translation can slowerwhen effective surfaces 810 a, 810 b and 810 c are positioned overregions that are farther away, (e.g., regions 612 a, 612 b, and 612 cand 614 a, 614 b, and 614 c) and faster when positioned over regionsthat are closer (e.g., regions 616 a, 616 b, and 616 c). Alternativelyor in addition to varying a translation rate, a flow rate of reactiongas(es) provided to hollow cathode sources 802 a, 802 b and 802 c isvaried in order to control the rate of deposition onto different regionsof surfaces 806 a, 806 b and 806 c, respectively. In some embodiments,system 800 is used to deposit second films (not shown) onto films 803 a,803 b and 803 c.

According to some embodiments, a hollow cathode system includes a numberof hollow cathodes sources arranged in series, such as described abovewith reference to FIG. 7, as well as a number of hollow cathode sourcesarranged in parallel, such as described above with reference to FIG. 8.FIG. 9 shows a schematic view of system 900, which includes multiplehollow cathodes for depositing films 903 a, 903 b and 903 c onsubstrates 904 a, 904 b and 904 c, respectively. System 900 includes afirst set of parallel hollow cathode sources 902 a, 902 b and 902 c anda second set of parallel hollow cathode sources 905 a, 905 b and 905 c.Hollow cathode sources 902 a and 905 a can have an effective surfacewith a shape in accordance with a curved portion of surface 906 a ofsubstrate 904 a. Hollow cathode sources 902 b and 905 b can have aneffective surface with a shape in accordance with a curved portion ofsurface 906 b of substrate 904 b. Hollow cathode sources 902 c and 905 ccan have an effective surface with a shape in accordance with a curvedportion of surface 906 c of substrate 904 c. In some embodiments,surfaces 906 a, 906 b and 906 c have substantially the same shape. Inother embodiments, surfaces 906 a, 906 b and 906 c have differentshapes.

Substrates 904 a, 904 b and 904 c can be positioned on supports 901 a,901 b and 901 c, respectively. In some embodiments, supports 901 a, 901b and 901 c include a translational mechanism, such as a conveyor beltsystem, for translating substrates 904 a, 904 b and 904 c, respectively,in directions 908 and/or 918. It should be understood that the numberand arrangement of hollow cathode sources shown in FIGS. 7, 8 and 9 arerepresentative of some embodiments and are not meant to represent allpossible numbers and configurations. In addition, the substrate surfaceshapes and corresponding effective surface shapes of the hollow cathodesources shown in FIGS. 7, 8 and 9 are not meant to represent allpossible shapes of substrate surfaces and effective surface shapes. Forexample, a substrate can have a surface with one or more curved portionsand one or more substantially planar portions. The hollow cathodesources can mimic an entire substrate surface shape or portions of thesubstrate surface.

FIG. 10 shows flowchart 1000 indicating a high level process fordepositing a film having a uniform thickness on a surface of a substratein accordance with described embodiments. At 1002, a substrate having anon-planar surface is positioned with respect to an effective surface ofa source of a deposition system. The effective surface has a non-planarshape in accordance with the non-planar surface of the substrate. Anon-planar surface is defined as having a three-dimensional surfacegeometry or topography that is not substantially planar. The non-planarsurface of the substrate can encompass substantially an entire surfaceof the substrate or can include one or more regions of the substrate. Insome embodiments, the non-planar surface has at least one curved region.In some embodiments, the substrate is a curved surface of a window orlens for an electronic device. In some embodiments, the film is an ARcoating or one layer of a multi-layered AR coating.

The source can be any suitable deposition source. For example, in asputter deposition system, the source can correspond to a sputtertarget. In a PECVD system, the source can correspond to an ion source,such as a hollow cathode source. The non-planar surface of the substratecan be positioned or aligned with respect to the effective such thatparticles emitted from the source deposit as a film on the non-planarsurface. In some embodiments, the substrate is supported and/orpositioned using a support. In some embodiments the support includes atranslational mechanism configured to translate the substrate withrespect to the source. In some embodiments, the translational mechanismis configured to translate the substrate before and after a depositionprocess. In some embodiments, the translational mechanism is configuredto additionally translate the substrate during one or more depositionprocesses.

At 1004, the source is caused to emit particles such that the particlesdeposit as a film on the non-planar surface. The particles can be anysuitable material capable of forming a film on the substrate. In asputter deposition system, the particles can correspond to materialsputtered from the sputter target. In a PECVD system, the particles cancorrespond to ions and/or other reactive chemical species of a plasma.Since the effective surface has a non-planar shape in accordance withthe non-planar surface of the substrate, the film has a substantiallyuniform thickness.

At 1006, after depositing the film, the source is optionally used todeposit one or more additional films, forming a coating having multiplelayers of film on the non-planar surface of the substrate. In someembodiments, the multiple layers of film make up an AR coating. In oneembodiment, the AR coating includes alternating films of Si₃N₄ and SiO₂films. In other embodiments, a different source is used to form the oneor more additional films. In some embodiments, the same source is usedto form the one or more additional films.

The foregoing description, for purposes of explanation, used specificnomenclature to provide a thorough understanding of the describedembodiments. However, it will be apparent to one skilled in the art thatthe specific details are not required in order to practice the describedembodiments. Thus, the foregoing descriptions of the specificembodiments described herein are presented for purposes of illustrationand description. They are not target to be exhaustive or to limit theembodiments to the precise forms disclosed. It will be apparent to oneof ordinary skill in the art that many modifications and variations arepossible in view of the above teachings.

What is claimed is:
 1. A method of depositing a film on a curved surfaceof a substrate, the method comprising: positioning the curved surfacewith respect to a source of a deposition system, wherein the sourceincludes an effective surface having a curved shape in accordance withthe curved surface of the substrate; and causing the source to emit aplurality of particles such that the plurality of particles becomedeposited on the curved surface as the film, wherein the curved shape ofthe effective surface is associated with a thickness uniformity of thefilm.
 2. The method of claim 1, wherein the deposition system is asputter deposition system and the source is a sputter target, whereincausing the source to emit the plurality of particles comprisesdirecting a sputter gas at the sputter target such that the plurality ofparticles are sputtered from the sputter target.
 3. The method of claim1, wherein the deposition system is a plasma enhanced chemical vapordeposition (PECVD) system and the source is a hollow cathode source,wherein causing the source to emit the plurality of particles comprises:supplying a reaction gas to the hollow cathode source, and causing thehollow cathode source to discharge a plasma having ions and/or otherreactive chemical species corresponding to the plurality of particles.4. The method of claim 3, wherein the deposition system includes one ormore hollow cathode sources, each hollow cathode source including aneffective surface having a curved shape in accordance with differentportions of the curved surface of the substrate.
 5. The method of claim4, wherein each of the hollow cathode sources has an effective surfacethat is a distance d from curved surface of the substrate, wherein thedistance d is substantially the same for each hollow cathode source. 6.The method of claim 1, wherein the film is an antireflective coating andcomprises one or more of Si₃N₄, SiO₂, NB₂O₅, TiO₂ and TaO₂.
 7. Themethod of claim 1, wherein the particles are a first type of particlesand the film is a first film, wherein the method further comprises:after causing the source to emit the plurality of the first type ofparticles, causing the source to emit a plurality of a second type ofparticles, different than the first type of particles, such that theplurality of the second type of particles become deposited on the firstfilm as a second film.
 8. The method of claim 1, further comprising:translating the substrate relative to the source during a depositionprocess such that the film is deposited on different regions of thecurved surface at a time.
 9. The method of claim 1, wherein thesubstrate is a first substrate, the film is a first film, and the sourceis a first source, the method further comprising: causing a secondsource to emit a second plurality of particles such that the secondplurality of particles become deposited on a curved surface of a secondsubstrate as a second film causing.
 10. The method of claim 9, whereinthe second film is deposited substantially simultaneously withdepositing the first film.
 11. The method of claim 1, wherein the filmis substantially transparent and the curved surface is a window or alens of an electronic device.
 12. A deposition system for depositing afilm on a surface of a substrate, the surface characterized as having anon-planar shape, the deposition system comprising: a source thatincludes an effective surface configured to emit a plurality ofparticles, wherein the effective surface has a non-planar shape inaccordance with the non-planar shape of the surface of the substrate;and a support configured to position the substrate with respect to thesource such that the plurality of particles emitted from the sourcedeposit as the film on the surface of the substrate, wherein thenon-planar shape of the effective surface is associated with a thicknessuniformity of the film.
 13. The deposition system of claim 12, whereinthe effective surface has a curved shape in accordance with a curvedshape of the surface of the substrate.
 14. The deposition system ofclaim 12, wherein the deposition system is a plasma enhanced chemicalvapor deposition (PECVD) system and the source is a hollow cathodesource.
 15. The deposition system of claim 12, wherein the depositionsystem is a sputter deposition system.
 16. The deposition system ofclaim 12, wherein the support includes a translation system configuredto translate the substrate relative to the source during a depositionprocess.
 17. The deposition system of claim 16, wherein the translationsystem positions different regions of the surface of the substratesufficiently proximate the source to deposit the film thereon.
 18. Thedeposition system of claim 17, wherein the translation system isconfigured to translate the substrate relative to the source during asecond deposition process to deposit a second film on the film after afirst deposition process is complete.
 19. A plasma enhanced chemicalvapor deposition (PECVD) apparatus for depositing a film on a curvedsurface of a substrate, the PECVD apparatus comprising: a hollow cathodesource that includes an effective surface configured to emit a pluralityof ions, wherein the effective surface has a curved shape in accordancewith a curved shape of the curved surface of the substrate; and asupport configured to position the substrate with respect to the hollowcathode source such that the plurality of ions emitted from the sourcedeposit as the film on the curved surface of the substrate, wherein thecurved shape of the effective surface is associated with a thicknessuniformity of the film.
 20. The PECVD apparatus of claim 19, wherein thesupport includes a translational mechanism that translates the substratewith respect to the hollow cathode source during a deposition process.